Processes for the elimination of nitrates from water by denitrification in microbiological reactors are already known. Such processes, carried out in rising current reactors containing a granular denitrifying biomass, have been described, for example, by Lettinga et al, Biotechnol. Bioeng. 22: 699-734 (1980), and by Timmermans, "Kinetics and Guidelines for the Design of Biological Denitrification Systems of Water" (1983 doctoral thesis; Catholic University at Louvain, Belgium).
For waste waters in particular, different reducing agents such as sugars, less expensive biodegradable organic material, and cellulose have been used, as have ethanol and methanol. For potable water, however, only the latter two have been used. All of these conventional reducing agents present the disadvantage that they dissolve in water and cause reduction in the quality of the potable water produced they must therefore be eliminated, by means of an additional, more expensive process at the end of the denitrification process.
One known denitrification process for potable water utilizes hydrogen, as described by Gros et al (1982) "Nitratentfernung aus dem Trinkwasser. Untersuchung von drei Verfahren in einer Pilotanlage in Zollikofen," Kurzbericht Gebr. SULZER (June, 1982).
According to this process, hydrogen gas is used as a reducing agent. Gaseous hydrogen is introduced at the bottom of a reactor and diffuses toward the top in the interior of the reactor. Water is displaced in the same direction. The biomass responsible for the denitrification process is retained in the interior of the reactor on mixing elements which take the form of small disks. While employing hydrogen as the reducing agent, this process does not permit the use of increased biomass densities, and allows a small but unacceptable quantity of nitrites to remain in the potable water.